The long-term objective of this project is to characterize the mechanisms by which human choriogonadotropin (hCG) and other hormones regulate steroid biosynthesis in cultured Leydig tumor cells. The specific aims are as follows: (1) identification of heterologous hormones that regulate hCG receptors; (2) characterization of the effects of receptor regulation on hCG actions; (3) elucidation of the mechanisms by which heterologous hormones regulate hCG receptors; (4)\characterization of the role of adenylate cyclase and protein kinases in the hormonal control of steroid biosynthesis; and (5) characterization of the mobilization of cholesterol used for steroid biosynthesis. Studies on these phenomena will be carried out using a combination of biochemical and genetic approaches and are expected to provide information about the regulation of polypeptide hormone receptors, gonadotropin action, and regulation of steroid biosynthesis. (C)